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#pragma once

#include <thrust/detail/config.h>

#if defined(_CCCL_IMPLICIT_SYSTEM_HEADER_GCC)
#  pragma GCC system_header
#elif defined(_CCCL_IMPLICIT_SYSTEM_HEADER_CLANG)
#  pragma clang system_header
#elif defined(_CCCL_IMPLICIT_SYSTEM_HEADER_MSVC)
#  pragma system_header
#endif // no system header

#if _CCCL_HAS_CUDA_COMPILER()
#  include <thrust/distance.h>
#  include <thrust/system/cuda/detail/execution_policy.h>
#  include <thrust/system/cuda/detail/fill.h>
#  include <thrust/system/cuda/detail/parallel_for.h>
#  include <thrust/system/cuda/detail/util.h>

THRUST_NAMESPACE_BEGIN

namespace cuda_cub
{
namespace __uninitialized_fill
{
template <class Iterator, class T>
struct functor
{
  Iterator items;
  T value;

  using value_type = thrust::detail::it_value_t<Iterator>;

  template <class Size>
  void _CCCL_DEVICE_API _CCCL_FORCEINLINE operator()(Size idx)
  {
    value_type& out = raw_reference_cast(items[idx]);

#  if _CCCL_CUDA_COMPILER(CLANG)
    // XXX unsafe. cuda-clang is seemingly unable to call ::new in device code
    out = value;
#  else
    ::new (static_cast<void*>(&out)) value_type(value);
#  endif
  }
};
} // namespace __uninitialized_fill

template <class Derived, class Iterator, class Size, class T>
Iterator _CCCL_HOST_DEVICE
uninitialized_fill_n(execution_policy<Derived>& policy, Iterator first, Size count, T const& x)
{
  // if the output type is trivially constructible from the input, it has no side effect, and we can skip placement new
  // and calling a constructor. Furthermore, if assigning the input value to an output element is also trivial, there is
  // no copy constructor which could have a side effect and we can delegate to fill_n (which uses
  // cub::DeviceTransform::Fill).
  using value_t = thrust::detail::it_value_t<Iterator>;
  if constexpr (::cuda::std::is_trivially_constructible_v<value_t, T const&>
                && ::cuda::std::is_trivially_assignable_v<value_t, T const&>)
  {
    cuda_cub::fill_n(policy, first, count, x);
  }
  else
  {
    cuda_cub::parallel_for(policy, __uninitialized_fill::functor<Iterator, T>{first, x}, count);
  }
  return first + count;
}

template <class Derived, class Iterator, class T>
void _CCCL_HOST_DEVICE uninitialized_fill(execution_policy<Derived>& policy, Iterator first, Iterator last, T const& x)
{
  cuda_cub::uninitialized_fill_n(policy, first, ::cuda::std::distance(first, last), x);
}

} // namespace cuda_cub

THRUST_NAMESPACE_END
#endif
